1. Field of the Invention
The present invention relates generally to an electronic push-button type door locking device for an automotive vehicle, and more particularly to an electronic door locking system by which vehicle doors can be locked or unlocked when the driver depresses a plurality of push-button type switches in accordance with a predetermined code.
2. Description of the Prior Art
The background of the present invention will be explained with respect to its application to the system used with an automotive vehicle.
As is well-known, there exists an electronic push-button type door locking system for an automotive vehicle, by which vehicle doors can be locked or unlocked when the driver depresses a plurality of push-button type switches installed at an appropriate position on the outside of an automotive vehicle in accordance with a predetermined code. When such an electronic vehicle door locking system as desccribed above is used to lock or unlock the doors, it is very convenient for the driver since the vehicle doors can be locked or unlocked by the driver without using the ignition key, in particular, when the vehicle is left parked.
In the above-mentioned electronic door locking system, however, there exists the danger that the doors will always be locked whenever the driver depresses the push-button type switches, even when the vehicle is left parked in a dangerous situation, for instance, such as when one of the vehicle doors is not closed perfectly or when the parking brake is not applied (when the gear shift lever is not set to Park position securely in the case of an automatic transmission type vehicle). In the case where the driver depresses the push-button switches to lock the vehicle doors with any one of the doors not closed perfectly, the door may be unlocked when the imperfectly-closed door is forcedly pushed inwardly; in the case where the vehicle is left parked without applying parking brake, the vehicle may move into an accident.
Further, in this connection, there exist some vehicles provided with indicator lights for warning that the doors are not closed perfectly or that the parking brake is not applied. However, in some cases, these lights do not come on when the ignition key is turned off or is not in the keyhole. Furthermore, although it is possible to check that all the vehicle doors are closed perfectly in dependence upon the fact that a light for lighting the passenger compartment is left turned on, there exists a danger that the driver may fail to notice it during the daytime.